Moraxella catarrhalis is a common cause of otitis media in children and of lower respiratory tract infections in adults with chronic obstructive pulmonary disease; therefore, these two groups would benefit from a vaccine to prevent M. catarrhalis infections. Moraxella catarrhalis is a Gram-negative diplococcus frequently found as a commensal of the upper respiratory tract. However, over the past 2 to 3 decades this bacterium has emerged from being considered as a harmless commensal to being recognized as a genuine respiratory tract pathogen of serious public health concerns.
Acute otitis media is the most common bacterial infection in children with 70% experiencing at least one episode by age 3. M. catarrhalis is the third leading cause of otitis media after Streptococcus pneumoniae and nontypeable Haemophilus influenzae. M. catarrhalis is associated with 25% of acute otitis media by culture and 46.4% of chronic middle ear effusion by PCR. In addition, the nasopharyngeal carriage rate of M. catarrhalis in children is high (up to 75%) and the frequency of colonization is positively related to the development of otitis media.
In adults, M. catarrhalis is the second most common bacterial cause of exacerbations of chronic obstructive pulmonary disease (COPD) after non-typeable H. influenzae. COPD is the fourth leading cause of death in the United States, affecting 24 million Americans. M. catarrhalis causes approximately 10% of exacerbations of COPD, accounting for 2 to 4 million episodes annually. Furthermore, M. catarrhalis also colonizes the lower respiratory tract in up to 2.5 to 10% of adults with COPD at their stable states. Lower airway colonization contributes to airway inflammation in COPD as a result of sloughing of highly inflammatory bacterial cell wall antigens into the airway.
M. catarrhalis is a nonencapsulated bacterium and does not secrete exotoxin. The current vaccine studies have mostly focused on various outer membrane proteins (OMPs) as vaccine candidates. To date, a limited number of OMPs have been examined and are currently under different stages of evaluation as part of an effort to develop a multicomponent vaccine against M. catarrhalis. 